line is already growing outside the supreme court, as the justices prepare to take up the issue of gay marriage. It will hear testimony on two laws this week, including california's proposition 8, which bans gay marriage, defining marriage as only between a man and a woman. It comes just days after former secretary of state hillary clinton released this video, supporting gay marriage. And tonight, a well-known architect of republican strategy is making news after weighing in on abc's "this week." I want to bring in rick klein with us. You saw this, too. Here's the straightforward answer from karl rove when george asked him this morning. Karl rove, can you imagine the ne republican candidate saying flatout, I'm for gay marriage? Ild. He quickly moved on to another issue right after that. But rove's team knew this was making headlines on a sunday night. They reached out to you before we came on the air? That's right. An important distinction that karl rove wants me to make. He sent me an e-mail, while he could see a republican candidate supporting gay marriage, that's not necessarily saying the nominee will do so. But here's the thing. The politics around gay marriage are changing and fast. It's been less than a year since president obama himself dropped his opposition to gay marriage in that interview with our colleague, robin roberts. And now, even some prominent republicans are settling on the same position. And, rick, you track the trend lines. What is the polling telling us right now? It is moving so fast. In 2004, during george w. Bush's re-election, we asked in a poll if gay marriage should be legal. And only 32% said yes. This month, that number is up to 58%. That's a tectonic shift.

This transcript has been automatically generated and may not be 100% accurate.